Field
Aspects of the present invention generally relates to a tomography system in which computed tomography (CT) is performed, particularly relates to a breast tomography system used to photograph a breast.
Description of the Related Art
In recent years, mammography apparatuses that take X-ray transmission images of breasts have been used for breast cancer tests. However, since images obtained by using the mammography apparatus are plan-view images, a tumor or a calcareous portion overlapping with tissue such as a mammary gland makes it difficult to detect an abnormal portion in some cases. There is known a breast tomography system that obtains a tomographic image of a breast by using the computed tomography to solve such a problem with a plan-view image.
The Specification of U.S. Patent Application Publication No. 2004/0081273 discloses a breast tomography system including an X-ray generation tube, an X-ray detector, and a gantry. The X-ray generation tube and the X-ray detector face each other and rotate around the imaginary rotation axis. The gantry stores the X-ray generation tube and the X-ray detector. The Specification of U.S. Patent Application Publication No. 2004/0081273 discloses that the X-ray generation tube is operated in such a manner that a breast is exposed to a cone beam at predetermined rotation angles to be irradiated with the cone beam. A plurality of X-ray transmission images are subsequently obtained by using the X-ray detector facing the X-ray generation tube and are subjected to reconfiguration, and a tomographic image of the breast is thereby obtained.
Note that the Specification of U.S. Patent Application Publication No. 2004/0081273 describes the X-ray generation tube including a rotary anode target and a circular pipe housing accommodating the X-ray generation tube and discloses that the tube axis of the X-ray generation tube and the longitudinal side of the housing are disposed to be perpendicular to a test bed.
However, the breast tomography system described in the Specification of U.S. Patent Application Publication No. 2004/0081273 discloses that a dead space of several tens of millimeters is produced between an emission window of the X-ray generation tube and a front panel of the gantry. The problem of the dead space is to be solved because the dead space causes a blind length, within which an X-ray transmission image is not obtained, on the chest side of the breast or causes unnecessary exposure of the chest to the X-ray through openings communicating with breast insertion portions.
The breast tomography system described in the Specification of U.S. Patent Application Publication No. 2004/0081273 provides a way of reducing the blind length in such a manner that recesses are disposed around the openings of the test bed. However, since an unnatural photographing posture of the subjectee is required to meet the recess shape of the front panel, further improvement in usability and further reduction in the blind length have been desired.